Over time and through repeated use, bones and joints can become damaged or worn. For example, repetitive strain on bones and joints (e.g., through athletic activity), traumatic events, and certain diseases (e.g., arthritis) can cause cartilage in joint areas, which normally provides a cushioning effect, to wear down. When the cartilage wears down, fluid can accumulate in the joint areas, resulting in pain, stiffness, and decreased mobility.
Arthroplasty procedures can be used to repair damaged joints. During a typical arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned or an implant can be implanted into the damaged region. Arthroplasty procedures may take place in any of a number of different regions of the body, such as a knee, a hip, a shoulder, or an elbow.
One type of arthroplasty procedure is a total knee arthroplasty (“TKA”), in which a damaged knee joint is replaced with prosthetic implants. The knee joint may have been damaged by, for example, arthritis (e.g., severe osteoarthritis or degenerative arthritis), trauma, or a rare destructive joint disease. Typically, a candidate for a TKA has significant wear or damage in tow or more “compartments” of the knee. The knee is generally divided into three “compartments, including: medial (the inside part of the knee), lateral (the outside part of the knee), and the patellofemoral (the joint between the knee cap and the thighbone). During a TKA procedure, a damaged portion in the distal region of the femur may be removed and replaced with a metal shell, and a damaged portion in the proximal region of the tibia may be removed and replaced with a channeled piece of plastic having a metal stem. In some TKA procedures, a plastic button may also be added under the surface of the patella, depending on the condition of the patella.
Another type of arthroplasty procedure is a unicompartmental (knee) arthroplasty or a partial knee replacement (“UKA”) in which only a portion (or a single compartment) of the knee is removed and replaced with prosthetic implants. Typically, a candidate for a UKA has significant wear or damage confined to primarily one compartment of the knee. A UKA may be a less invasive approach than a TKA and may have a quicker recovery time. A UKA may be utilized to prevent the spread of disease, such as in the early stages of osteoarthritis where the disease has only affected a portion of the knee and it is desirable to prevent the disease from spreading to other portions of the knee.
Implants that are implanted into a damaged region may provide support and structure to the damaged region and may belp to restore the damaged region, thereby enhancing its functionality. Prior to implantation of an implant in a damaged region, the damaged region is prepared to receive the implant. For example, in a knee arthroplasty procedure, one or more of the bones in the knee area, such as the femur and/or the tibia, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) to provide one or more surfaces that can align with the implant and thereby accommodate the implant.
Accuracy in implant alignment is an important factor to the success of a TKA or UKA procedure. A one to two millimeter translational misalignment may result in imbalanced ligaments and thus may significantly affect the outcome of the procedure. For example, implant misalignment may result in intolerable post-surgery pain and also may prevent the patient from having full leg extension and stable leg flexion.
To achieve accurate implant alignment, prior to treating (e.g., cut, drilled, reamed, and/or resurfaced) any regions of a bone, it is important to correctly determine the location at which the treatment will take place and how the treatment will be oriented. In some methods, an arthroplasty jig may be used to position and orient a resection or sawing instrument, such as a cutting, drilling, reaming, or resurfacing instrument on the regions of the bone. The arthroplasty jig may, for example, include one or more apertures and/or slots that are configured to accept such an instrument. However, under some methods, it is difficult to determine the proper orientation of an arthroplasty jig and more specifically, of a unicompartmental arthroplasty jig. Some methods utilize customized arthroplasty jigs to provide orientation of the treatment relative to the regions of the bone. However, such jigs often rely on a human to subjectively determine or “eyeball” rotational angles and the extent of the treatment. For example, when performing a resection in a knee region of a patient femur and/or tibia, many jigs rely on a surgeon to determine the proper orientation of the jig as well as how much of the bone to remove. In other words, once a surgeon has begun cutting to perform a resection, it is often difficult to accurately stop the cut.
Accordingly, there is a need in the art for customized arthroplasty cutting guides and surgical methods of using such cutting guides that increases the accuracy of arthroplasty procedures.